The researchers looked at information from a very large database of breast cancer patient information called the National Cancer Data Base. They reviewed the records of people diagnosed with breast cancer between 1998 and 2007. Slightly less than 1% of all breast cancer cases reviewed were men: 13,457 male breast cancer cases were reviewed and 1,439,866 female breast cancer cases were reviewed.

Survival in the 5 years after diagnosis was:

74% for men

83% for women

The lower breast cancer survival rate in men was only seen in people diagnosed with early-stage breast cancer. For people diagnosed with advanced-stage breast cancer, survival was about the same for men and women. Advanced-stage breast cancer is cancer that has spread to non-breast tissue in the breast area (locally advanced cancer) or to parts of the body away from the breast (metastatic cancer).

Five year survival for advanced-stage breast cancer was:

16% for men

19% for women

On average, the breast cancer stage at diagnosis was higher in men compared to women. When diagnosed, breast cancers in men tended to be:

larger in size

higher grade, which relates to how aggressive the cancer cells are

spread to nearby lymph nodes

Breast cancers in men also weren’t always treated the same way as the disease in women, though the researchers aren’t sure why. For example:

Breast cancer in men was more likely to be hormone-receptor-positive (88% in men vs. 78% in women), but men were less likely than women to get hormonal therapy as part of their treatment plan. Hormone-receptor-positive breast cancers are cancers that depend on the hormone estrogen to grow and spread (men make estrogen, too, just not as much as women). By blocking estrogen’s effects or limiting how much is made in the body, hormonal therapy can help treat hormone-receptor-positive breast cancer and make it less likely that the cancer will come back.

Radiation therapy after surgery was less common in men than women. Radiation therapy is often given after breast cancer surgery to reduce the risk that the cancer will come back in the breast area (local recurrence).

There are several possible reasons for the differences found in this study, including:

Genetic or biological differences between the breast cancers in men and the breast cancers in women. This means that male breast cancers may develop, grow, and spread differently than female breast cancer. Breast cancer in men also may respond differently to treatment than breast cancer in women.

Differences in when breast cancer is diagnosed. Diagnosing early-stage breast cancer in men may take longer compared to diagnosing similar cancers in women. This may be in part because awareness of breast cancer in men is very low.

Differences in treatment needs. Because breast cancer is rare in men, it's hard to study the best way to treat it. Most male breast cancer treatments are modeled on treatments for women. A different approach may be needed.